Environmental Protection Agency chief Lisa Jackson announced Thursday that she’s stepping down after a four-year tenure marked by her agency’s first greenhouse gas regulations and repeated battles with industry groups and GOP lawmakers.

Jackson, the first African American to serve as EPA administrator, came into office with bold plans to address climate change but accomplished only part of her agenda, foiled by opposition on Capitol Hill and occasionally the White House.

She often faced harsh congressional grilling. Last year, the GOP chairman of the House Energy and Commerce Committee, Michigan Rep. Fred Upton, said she would need her own parking spot at the Capitol because he planned to summon her often for questioning.